1.Synthetic Studies on Kalihinane-type Diterpenoid Kalihinene X and Kalihinol A.Kalihinane-type diterpenoid possessing cis-or trans-decalin and tetrahydropyran or tetrahydrofuran as its fundamental skeleton, is a highly functionalized marine diterpenoid, bearing isocyano, isothiocyanato, formamide, hydroxy and/or chlorine groups. Kalihinene X is a kalihinane-type diterpene formamide having cis-decalin and chlorinated tetrahydropyran moieties. Kalihinol A is a kalihinane-type diterpene isocyanide having trans-decalin and chlorinated tetrahydropyran moieties. For efficient synthesis of both compounds, the synthesis was carried out through common synthetic intermediate cis-decalin derivative. Total synthesis of kalihinene X involves regioselective coupling reaction of carbanion of alkyl sulfone with epoxyalcohol and synthesis of common synthetic intermediate cis-decalin derivative by intramolecular Diels-Alder reaction. The absolute configuration of kalihinene X could be determined by this total synthesis. The cis-decalin derivative was converted to trans-decalin derivative which is synthetic precursor of kalihinol A.2.Synthetic Studies on Marine Terpenoid Elisabethin C and Elisapterosin B.Elisabethin C is a novel bicyclic bisnor-diterpenoid which was isolated from the gorgonian Pseudopterogorgia elisabethae. Elisapterosin B is a novel tetracyclic diterpenoid which was isolated from the same gorgonian. For efficient synthesis of both compounds, the synthesis was carried out through common synthetic intermediate bicyclo[4.3.0]nonane derivative. Total synthesis of elisabethin C was successfully carried out by stereoselective synthesis of bicyclo[4.3.0]nonane derivative, which is the common synthetic intermediate, with Dieckmann cyclization as the key step. The absolute configuration of elisabethin C was determined based on this total synthesis. The bicyclo[4.3.0]nonane derivative was converted to tricyclic compound which is synthetic precursor of elisapterosin B.